Added a #define so MSVC will in turn #define.

zsnes/src/zloader.c

@@ -24,6 +24,7 @@ Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 #include "gblhdr.h"
 #define DIR_SLASH '/'
 #else
+#define _POSIX_
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

zsnes/src/zmovie.c

@@ -25,6 +25,7 @@ Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 #define DIR_SLASH "/"
 #define WRITE_BINARY "w"
 #else
+#define _POSIX_
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>